Cognitive radio technologies are key technologies for currently solving a contradiction between supply and demand of a wireless spectrum and increasing a spectrum utilization rate. A dynamic spectrum access mode allows a secondary user to access an idle authorized spectrum opportunistically, thereby alleviating the shortage problem of spectrum resources. In a cognitive radio network, a primary user shall use an authorized spectrum with a priority higher than that of the secondary user. To avoid affecting normal communication of the primary user, the secondary user needs to perceive spectrum availability before accessing channels, and then adopts an underlay or overlay spectrum sharing mechanism for coexistence with the primary user.
A primary link of realizing network construction and communication by the cognitive radio network is that neighborhood secondary users can find the other party mutually, and access a common available channel to conduct data transmission. This process is channel rendezvous, and is a precondition for realizing steps of communication handshake, message exchange, topology control, routing maintenance and the like by the neighborhood users.
According to a need for maintaining a dedicated common control channel in the network, a channel rendezvous strategy is classified into two categories currently: a channel rendezvous strategy with auxiliary common control channel and a blind channel rendezvous strategy without auxiliary common control channel. Although the channel rendezvous method with auxiliary common control channel can simplify the process for realizing channel rendezvous between the secondary users, the common control channel is easy to be occupied by the primary user in the cognitive radio network so that availability of the common control channel cannot be ensured at any time, thereby blocking rendezvous between the secondary users. In addition, the common control channel may bring the problem of single-point failure due to easy interference by malicious users. The blind channel rendezvous strategy does not need to maintain the common control channel, is a channel rendezvous strategy based on frequency hopping sequences of channels, makes full use of excellent channel switching performance of a cognitive radio device and can increase diversity of rendezvous channels, thereby avoiding defects of the common control channel. The blind channel rendezvous strategy is a channel rendezvous technology in general use. The channel rendezvous strategy technology based on frequency hopping sequences of channels is performed on a time division multiple access (TDMA) system. Each secondary user generates own frequency hopping sequences of channels according to a predefined sequence construction method. The sequence determines the channel access sequence of the secondary user. Once a pair of neighborhood users switches to the same available channel in the same time slot through channel frequency hopping within a communication range, rendezvous is successfully achieved. The frequency hopping sequences of the channels comprise a clock synchronization-constrained synchronous sequence and a clock synchronization-unconstrained asynchronous sequence. Apparently, the latter has wider applicability. To this end, designed frequency hopping sequences of channels shall ensure rendezvous under the condition that a clock offset of a frequency hopping node is arbitrary. In addition, to prevent rendezvous channels from generating problems of saturation and congestion, the feature of diversity of the channels in the cognitive radio network shall be fully used, so that rendezvous opportunities are uniformly distributed on all channels in the network, thereby ensuring accessed fairness of the channels. However, the secondary users using the frequency hopping method need to frequently switch the channels in order to achieve balanced channel load, causing large time consumption. Thus, the designed frequency hopping sequences shall achieve deterministic rendezvous in the shortest possible time.
At present, most of studies on channel rendezvous consider to configure omnidirectional antennas for the secondary users, i.e., signals are transmitted in all directions within an antenna communication range. In this way, primary users within the entire antenna signal coverage range may be disturbed, as shown in FIG. 1a. To reduce disturbance, directional antennas are configured, i.e., the signals are only transmitted in a certain specific direction. This is a promising communication technology, as shown in FIG. 1b. However, for a rendezvous problem under a directional antenna scenario, the difficulty is that antenna directions of a pair of neighborhood users must be opposite and the same channel is accessed to realize possible rendezvous; otherwise, rendezvous cannot be achieved even within a range of mutual communication. Thus, the present invention will be achieved in two steps: in the first step, directional antennas facing any direction initially are rotated to positions to face the other party mutually as soon as possible; and in the second step, the receiver and the sender switch the channels in accordance with predefined deterministic frequency hopping sequences to access the common available channel as soon as possible.